Push button elevator control system



ug. 28, 1934. Hl B GQLDMAN 1,972,015

RUSH BUTTON ELEVATOR CONTROL SYSTEII Filed July 20, 1932 L- Ll'l'flif'32 55 34 M@ me; A

Fifi@ T l Patented Aug. 28, 1934 Unirse STATES tenais PATENT PUSH BUTTONELEVATOR CONTROL SYSTEM 21 Claims.

lViy invention relates to pushbutton control systems for electricelevators, and it has particular relation to certainhereinafter-mentioned improvements which, while not limited to anyparticular use, are primarilyand especially adapted for hold-down orconstant-pressure pushbutton control systems in which the pushbuttonmust be pressed down constantly as long as the elevator is to run. Bythe term elevator I mean to include a vertically moving cage, car orplatform for' freight, passenger or dumbwaiter use.

One of the objects of my invention is to provide a non-interferenceswitch adapted for a constant-pressure pushbutton control-system forelevators, in order to safeguard the persons using the elevators, so asto give them time to load and unload, vAccording to my invention, thenon-interference switch-contacts are in series with the landingpushbuttons, as in my pending application Serial No. 408,982, ledNovember 22, 1929,v for Automatic elevator controls. Theseswitch-contacts are openedv whenever the elevator motor is energized,but first they are shunts ed by an auxiliary contact-device which wasnot provided in my pending application abovementioned. Theshunt-connected auxiliary contact-device keeps the landing pushbuttonslive so that a constant-pressure control system may be used. As soon asthe elevator-motor is deenergized, theY auxiliary contact-deviceinstantly opens, and the non-interference switch begins to`close, beingretarded by a dash-pot or the like, meanwhile killing the landingpushbuttons and giving the operator time to load or unload, or time toopen a rguard-device which automatically locks out the elevator-motorcontrols.

Another object of my invention is to provide a non-interference switchwhich is mechanically interlocked with the reversing contactors of anelectric elevator system of the constant pressure pushbutton type,

A further object of my invention is to provide elevator control systemutilizing barriers or guard-devices, the opening of which will lock outthe elevator motor so that the elevator-car cannot be moved until thebarrier is manually closed, supplemented by means of automaticallyringing alarm whenever someone depresses a button at another landingwhen the barrier at the elevator-car has been leftv open, so that theoperator at the car-landing will close the barrier again.

With the foregoing and other objects in View, my invention consists inthe elements, combinations, systems and methods hereinafter describedand claimed, and illustrated in the accompanying drawing, wherein Figure1 is a simplified diagrammatic View of circuits and apparatusillustrating a preferred form of embodiment of my invention, and

Figs. l2 and 3 are similar views showing modiiications.

An elevator car is raised and lowered by a reversible electric motor 2,shown as a threephase induction motor, which is controlled by two mainup and down electromagnetic reversing contactors U and D for energizingit in either direction of rotation. The accelerationof the motor, onstarting,r may be controlled by two starting resistances 5, which may becut out by an accelerating relay 6 energized from a timing relay 7. Themotor may be stopped by the usual brake, as shown, for example, in myaforementioned pending application.

Each of the reversing contactors U and D has an energizing coil 8, twomain contacts 9 for the motor circuit, a normally open auxiliary contactl1, and preferably also a normally closed auxiliary contact 12, althoughthe latter may be omitted if the contactors are provided, as is common,with electrical or mechanical interlocks for preventing the simultaneousactuation of both contactors, as indicated at 13.

Current is supplied to the contactor-coils 8 from the supply-line lthrough a switch 16 having an auxiliary contact 17 for the contactorcoilcircuit. An overspeed switch 18 on the motor shaft is also included inthecontactor-coil cirouit,vas well as a nal up limit switch 19, a finaldown limit switch 29, a car-gate Contact 21 and a car safety switch 22.

One of the supply-leads 23 of the contactorcoil circuit is connected toa control-means in the car, preferably one which cannot be moved to theup and down positions at the same time, being either a car switch ormechanically interlocked up and down pushbuttons 24 and 25, preferablyhaving a mechanical interlock 26 for preventing both buttons from beingdepressed at the same time.

In the normal at rest position of the controlmeans 24 and 25 in the car,a circuit is completed to a landing-pushbutton supply-lead 27 leading toa plurality of up and down landing pushbuttons 29 and 30, each landinghaving one up pushbutton and one down pushbutton.

The up pushbuttons 24 and 29 in the car and at the landings, whendepressed, connect the supply-'lead 23 to an up conductor 31 which leadsto the electromagnet-coil 8 of the up contaeter U, through an up stoplimit switch 32. The down pushbuttons and 30, when depressed, connectthe supply-lead 23 to a down conductor 33 which leads to theelectromagnetcoil 8 of the down contactor D, through a down stop limitswitch 34. The car pushbuttons 24 and 25 are so arranged that, wheneither one is actuated, the landing-pushbutton supplylead 27 isdeenergized, as shown.

The arrangement just described is what I call a constant-pressure orhold-down pushbutton control, in which the up or down contactor U or D,which energizes the motor 2, isA

held closed only as long as the pushbutton is held down. Suchconstant-pressure control systems, lacking the automatic controlfeatures which are provided for some elevators, are inherently lessexpensive than the automatic systems, and every eort must be made tokeep down the expense by using the simplest possible control circuit andapparatus.

As pointed out in my above-mentioned'automatic elevator control case,Serial No. 408,982, it is desirable to provide a non-interference switchto kill the landing pushbuttons for a few seconds after the car stops,so ask to prevent anyone else from interfering with the operatorscontrol over the car before he has time to enter or leave the car or tooperate a door or barrier such as the above-mentioned car-gate contact21 which opens and thus kills all control over the elevator-*noten Whenan efort is made to apply a non-interference switch to aconstant-pressure elevator control, difficulty is involved because ofthe vnecessity for keeping the landing pushbuttons 29 and 30 live untilthe motor stops, because the motor cannot'be kept going if vthepushbutton circuit is interrupted. Furthermore, economic considerations,as above pointed out, lead to a Vdesire for as few relays as possible,even avoiding the necessity for the electromagnetic or relay-type ofnon-interference switch which is shown in my above-mentioned pendingapplication.

In view of the foregoing considerations, I have devised a mechanicalnon-interference switch and I have shunted its contacts 37 byY means ofthe normally open auxiliary contacts 11 on the reversing contactors Uand D. When the normally closed contacts 12 are utilized, the normallyopen contact l1 of each contactor is connected in series with thenormally closed contact 12 of the other contactor, so that there can beno possibility of erroneous operation. l

The non-interference switch-contacts v37 are connected in series withthe landing-pushbutton supplf-iead V2'?. f

The non-interference switch 36 is'operated by means of a mechanicalconnection to the two reversing contactors U and D, preferably includingresilient connections or springs: 41, 42, carried by the respectivecontactors, so that, when either contactor is raised or energized, itlifts the non-interference switch 36 and opens the contacts 37. Themechanical connection is such, however, that before the contacts 37 aireopened the normally open auxiliary contact ll of the actuated contactor'is closed, so that a shtmting circuit is made around the contacts 37 inorder toavoid even a momentary break inthe pushbutton circuit. This isan importantprecaution in a'constant-pressure pushbutton system, asabove described. l

The non-interference switchg36 is provided with a dashpot 44 orequivalent time-delay device for retarding its action, and this devicemay retard the switch more strongly when it is closing than when it isopening, as indicated by the inclination of the piston-packing in thedrawing.

When the energized reversing contactor U or D is deenergized, itimmediately drops, thus permitting the non-interference switch to beginto drop,'moving slowly on account of the dashpot. However, the auxiliarycontact 11, which was closed when the contactor was energized, isimmediately opened, so that the landing-pushbutton-circuit is openedduring the time required for the non-interference switch-contact 37 toclose, thereby safeguarding the operator as previously described.

It is noted that my use of a mechanical nonvinterference switch, insteadof an electromagnetic-non-interference relay, may be applied toautomatic, as well as constant-pressure, pushbutton control systems.

In addition to, or instead of, the car-gate contact 21 alreadymentioned, I prefer to use landing doors or barriers, carrying switchesor contacts which are all connected in series, so that I the elevatorcannot be operated unless all barriers are properly closed, and I alsodesire to provide signal means that will operate, without any additionalwiring or equipment, (so as to cut down expense), whenever a landingpushbutton 29 or 30 is depressed, to summon the elevator car, when oneor more of the barriers or doors are open.

To this end, I provide a door-contact relay 52 which performs the doublefunction of placing a i break in the up and down contactor-coilcircuits, when one door or barrier is open, and transferring theenergizing circuit from the up or down contactor-coil 8 to a bell orother signal54, when one door or barrier is open.

The door-contact or barrier-contact relay 52 is provided with anactuating coil 53 which is energized whenever all of the door contacts50 are closed. This causes the relay to pick up, closing two normallyopen contacts 55 and 56 which are in series with the "up and downconductors 31 and 33, respectively, for the two contactorcoils -8, andat the same time opening two normally closed contacts 57 and 58 whichare connected between the bell or signal device 54 and said up and downconductors 31 and 33, respectively.

When the door-contact relay 52 is not properly energized, the up anddown conductors 31 and 33 are thus caused to actuate the bell 54, in-

stead of actuating the contactor-coils 8, so that when a pushbutton isdepressed under these circumstances the bell automatically rings, thussummoning the person who left the door open,

so that he will close the door and permit someone j vide, for theprotection of the operator in the fa.

car,- anemergency-release switch 59 in the car, which must be held downto be effective, and which will short-circuit all ofthe door contactsandkeep the operator from being stuck between two landings.

However, j, L -4 It will be noted that my double-purpose doorcontact andsignal relay 52 not only avoids the use of extra equipment forsignalling purposes, but it also avoids the necessity for a separatecircuit for the sole purpose of signalling, which, under unionregulations, could not be installed by the elevator Workmen, but must beinstalled by electricians, and, according to some safety codes, must usewires lying in separate conduits. All of these difiiculties, as well asimproved automatic and instantaneous signalservice, are obtained by myrelay 52 which avoids the necessity for a separate signalling pushbuttonat each landing.

While I have shown and described my invention in a preferred form ofembodiment, I do not desire to be limited altogether thereto. Forexample, in dumb-waiters, the control equipment 2e and 25 in the carwould be omitted, as well as the car-gate contact 21 and the car safetyswitch 22, The foregoing and other changes can be made without departingfrom the essential spirit of my invention. I desire, therefore, that myappended claims shall be accorded the broadest interpretation consistentwith their language and the prior art.

As another exemplary modification, it may sometimes be desirable toprovide landing pushbuttons so arranged that, if the car is at the topof its shaftway, and two or more down buttons are pressed at differentlandings at the same time, the car will stop at the last button reached,when it is released, regardless of how the down buttons are actuated athigher landings, and if the car is in the basement and two or more upbuttons are pressed at dii'erent landings at the same time, the car willstop when the lowest button is released, instead of keeping on travelinguntil the last up landing button is released, as in Fig. 1.

For this purpose, I may provide long-stroke, double-contact up and downbuttons 61 and 62 at the landings, as shown in Fig. 2, connecting themso that the energizing current, after passing through thenon-interference switch 37, is led irst to the top and bottom contactsof one of the buttons, as 62, at the lowest landing, then from the topcontacts of this button to the top and bottom contacts of theotherbutton 61 at the same landing, then from the top contacts of thelast-mentioned button to the top and bottom contacts of one of thebuttons of the next higher landing, and so on through all the landingbuttons. The bottom contacts of the down buttons 62 at the landings leadto the down conductor 33 which supplies the down contactor as in Fig. 1,whe the bottom contacts of the up buttons 61 at the landings, in Fig. 2,lead to the up conductor 31. Long-stroke buttons 61 and 62 will have tobe used to provide time, after a button 61 or 62 has been released, forthe main up and down contacter, as the case may be, to drop down,thereby open-circuiting the auxiliary non-interference contacts 11 andkilling all of the landing buttons before the top contacts of thereleased buttonl are closed so as to energize the buttons at the higherlandings.

1f it desired to have the elevator stop at the nrst down button that isreached on descendiing in response to a call from a plurality oi landing'out-tons, instead of continuing on to the bottom one, as in Fig. 2, 1may utilize the connections shown in 3, wherein the supply currentcoming from the non-interference switch 37 goes to the up button y51 atthe lowest landing, and

thence on through the other up buttons 61, in order, as indicated at 71,While a branch circuit 72 leads from the non-interference switch 37 andgoes rst to the down button 62 at the top landing, and thence on throughthe other down buttons 62, in order, as indicated at 73.

I claim as my invention:

1. A pushbutton elevator-control system; comprising, in combination withan elevator car and a reversible electric elevator motor;electromagnetic up and down reversing contactors, energizing means forthe energizing coils of said reversing contactors, said energizing meanscomprising a source oi supply and control circuits including pushbuttonsat the landings; a delayed-action non-interference switch havingcontacts in series with the energizing circuits for said landingpushbuttons, means responsive to the energization of either of saidreversing contactors for rst closing a by-pass circuit around saidnon-interference switch-contacts and then causing said non-interferenceswitch-contacts to open, and for respondng to the deenergization of theenergized contactor for opening said by-pass circuit and then causingsaid non-interference switchcontacts to close only after a predeterminedtimedelay.

2. A pushbutton elevator-control system; cornprising, in combinationwith an elevator car and a reversible electric elevator motor;electromagnetic up and down reversing contactors having energizingcoils, main contacts for the elevator motor circuit, a normally closedauxiliary contact and a normally open auxiliary Contact; energizingmeans for the energizing coils of said reversing contactors, saidenergizing means comprising control circuits including pus'nbuttons atthe landings and control means in the car; and non-interference meansfor giving the user of the elevator time to enter or leave the car afterit has reached its landing before anyone else can summon the car fromanother landing; characterized by said non-interference means comprisinga delayed-action relay having normally closed contacts which open aftera slight delay 7" when either of said reversing contactors is actuatedand which close after a longer delay when the actuated contacter isreleased, said delayed-action relay-contacts being in series with thelanding bushbuttons and being shunted by the normally closed auxiliarycontact of the up contactor in series with the normally open auxiliarycontact of the down contactor, and being also shunted by the normallyopen auxiliary contact of the up contactor in series With the normallyclosed auxiliary contact oi the down contacter.

3. A constant-pressure pushbutton elevatorcontrol system; comprising, incombination with an elevator car and a reversible electric elevatormotor; electromagnetic up and down reversing contactors; control meansin the car for energizing either of said reversing contactors at willand vlor instantly discontinuing the energization thereof upon thereturn of said control means to its normal inoperative position; andconstantthen causing said non-interference switch-contacts to open, andforresponding to the denergization of the energized contactor foropening said by-pass circuit and then causing said noninterferenceswitch-contacts to close only after a predetermined time-delay.

4. A pushbutton elevator-control system; comprising, in combination withan elevator car and a reversible electric elevator motor;electromagnetic up and down reversing contactors having energizingcoils, main contacts for the elevator motor circuit, and a normally openauxiliary contact; energizing means for the energizing coils ofY saidreversing contactors, said energizing means comprising control circuitsincluding pushbuttons at the landings, a retarded noninterference switchhaving contacts in series with the energizing circuits for said landingpushbuttons, connections for connecting each of the normally openauxiliary contacts of the two reversing contactors in parallel to saidnon-interference switch, means responsive to the energization of eitherof said reversing contactors for causing said `non-interferenceswitch-contacts to open after the closure of one of said shuntingauxiliary contacts, and means responsive to the deenergzation of theenergized contactor for causing said non-interference switch-contacts toclose only after a predetermined time-delay.

5. A pushbutton control-system for an electric elevator comprising acar, barriers for the safeguarding of people, and barrier-operatedswitches for the prevention of elevator-movement when said barriers arenot properly positioned, characterized by electromagnetic up and down"reversing contactors; up and down pushbuttons at the landings forenergizing said up and down contactors, respectively; and a retardednon-interference switch having contacts in series with the energizingcircuits for said landing pushbuttons, means responsive to theenergize.- tion of either or' said reversing contactors for rst closinga by-pass circuit around said non-interference switch-contacts and thencausing said non-interference switch-contacts to open, and forresponding to the deenergization of the energized contactor for openingsaid by-pass circuit and then causing said non-interferenceswitch-contacts to close only after a predetermined timedelay sufcientfor the person in control of the elevator to operate one of saidbarriers.

6. The invention as specified in claim 5, characterized by abarrier-contact relay having an energizing coil in series with aplurality of said barrier-operated switches, whereby said barriercontactrelay is energized only when said serially connected barrier-operatedswitches are all closed, said barrier-contact relay having normally opencontacts connected in series with an energizing circuit of both of thereversing contactors, so as to prevent the operation of eithercontacter' when one or more of the barriers are improperly positioned,and signal means connz'ted to be effectively energized in lieu of the.up or down reversing contacter when a pushbutton is depressed While thebarrier-contact relay is deenergized.

7. The invention as specied in claim 5, characterized by abarrier-contact relay having an energizing coil in series with aplurality of said barrier-operated switches, whereby said barriercontactrelay is energized only when said serially connected barrier-operatedswitches i are Yall closed, said barrier-contact relay having a pair ofnormally openV main contact circuits'connected in series with therespective energizing circuits of the up and down reversing contactors,and a signal means, said barrier-contact relay having a vpair ofauxiliary contact circuits which are closed when said barrier-contactrelay is unenergized, for completing an energizing circuit from the upand down pushbutton circuits to said signal means to energize the latterwhenever a pushbutton is depressed when one of said serially connectedbarrier-operated switches is open.

8. A pushbutton control-system for an electric elevator comprising acar, barriers for the safeguarding of people, and barrier-operatedswitches for the prevention of elevator-movement when said barriers arenot properly positioned, characterized by electromagnetic up and downreversing contactors; up and down pushbuttons at the landings forenergizing said up and down contactors, respectively; a barrier-contactrelay having an energizing coil in series with a plurality of saidbarrier-operated switches, whereby said barrier-contact relay isenergized only when Vsaid serially connected barrier-operated switchesare all closed, said barriercontact relay having -apair of normally openmain contact circuits connected in series with the respectiveenergizingcircuits or" the up and down reversing contactors, .and a signal means,said barrier-contact relay having a pair or" auX- iliary contactcircuits which are closed when said barrier-contact relay isunenergized, for completing .an energizing circuit from the up and fdownpushbutton circuits to said signal means to energize the latter whenevera pushbutton is depressed when one of said serially connectedbarrier-operated switches is open.

9. A pushbutton control-system for an electric elevator comprising acar, barriers for the safeguarding of people, and barrier-operatedswitches for the prevention of elevator-movement when said barriers arenot properly positioned; characterized by electromagnetic up and downreversing contactors; up and down pushbuttons at the landings forenergizing said up and down contactors, respectively; a signal means;and means responsive to an open position of one or more barrier-switchesfor making an energizing circuit connection from one or more landingpushbuttons to said signal means.

10. A pushbutton control-system for an electric elevator comprising acar, barriers for the safeguarding of people, and barrier-operatedswitches for the prevention of elevator-movement when said barriers arenot properly positioned; characterized by electromagnetic up and downreversing contactors having energizing coils, energizing means for theenergizing coils of said reversing contactors, said energizing meanscomprising control circuits including pushbuttons at the landings, and aretarded non-interference switch having contacts in series with theenergizing circuits for said landing pushbuttons, means responsive tothe energization of either of said reversing contactors for firstclosing a bypass circuit around said non-interference switchcontacts andthen causing said non-interference switch-contacts to open, and forresponding'to the deenergization oi the energized contactor for openingsaid by-pass circuit and then` causing said non-interferenceswitch-contacts to close only after a predeterminedtime-delay suiicientfor the person in control of the elevator to operate one of saidbarriers.

, 11. The invention as specified in claim l0, characterized by abarrier-contact relay having an ifi() energizing' coil in series with aplurality of said barrier-operated switches, whereby said barriercontactrelay is energized only when said serially connected barrier-operatedswitches are all closed, said barrier-contact relay having normally opencontacts connected in series with an energizing circuit of both of thereversing contactors, so as to prevent the operation of either contactorwhen one or more of the barriers are improperly positioned, and signalmeans connected to be eiectively energized in lieu of the up or downreversing contactor when a pushbutton is depressed while thebarrier-contact relay is deenergized.

l2. The invention as specied in claim l0, characterized by abarrier-contact relay having an energizing coil in series with aplurality of said barrier-operated switches, whereby said barriercontactrelay is energized only when said serially connected barrier-operatedswitches are all closed, said barrier-contact relay having a pair ofnormally open main contact circuits connected in series with therespective energizing circuits of the up and down reversing contactors,and a signal means, said barrier-contact relay having a pair orauxiliary contact circuits which are closed when said barrier-contactrelay is unenergized, for completing an energizing circuit from the upand down pushbutton circuits to said signal means to energize the latterwhenever a pushbutton is depressed when one of said serially connectedbarrier-operated switches is open.

13. A pushbutton control-system for an electric elevator comprising acar, barriers for the safeguarding of people, and barrier-operatedswitches for the prevention of elevator-movement when said barriers arenot properly positioned; characterized by electromagnetic up and downreversing contactors having energizing coils; energizing means for theenergizing coils of said reversing contactors, said energizing meanscomprising control circuits including pushbuttons at the landings; abarrier-contact relay having an energizing coil in series with aplurality of said barrier-operated switches, whereby said barriercontactrelay is energized only when said serially connected barrier-operatedswitches are all closed, said barrier-contact relay having a pair ofnormally open main contact circuits connected in series with therespective energizing circuits of the up and down reversing contactors,and a signal means, said barrier-contact relay having a pair ofauxiliary Contact circuits which are closed when said barrier-contactrelay is unenergized, for completing an energizing circuit from the upand down pushbutton circuits to said signal means to energize the`latter whenever a pushbutton is depressed when one of said seriallyconnected barrier-operated switches is open.

lll. A pushbutton control-system for an electric elevator comprising acar, barriers for the safeguarding of people, and means includingbarrieroperated switches for the prevention of elevatormovement whensaid barriers are not properly positioned; characterized by means,including electromagnetic up and down reversing contactors havingenergizing coils, for controlling the operation of the car; energizingmeans for the energizing coils of said reversing contactors, saidenergizing means comprising control circuits including pushbuttons atthe landings; a signal means, and means responsive to an open positionof one or more barrier-switches for making an energizing circuit fromone or more landing pushbuttons to said signal means.

l5. The invention as specified in claim 4, characterized by a mechanicalconnection between said non-interference switch and the reversingcontactors whereby said non-interference switch is lifted whenevereither one of the reversing contactors is lifted into energizedposition.

16. A pushbutton elevator-control system; comprising, in combinationwith an elevator car and a reversible electric elevator motor;electromagnetic up and down reversing contactors, energizing means forthe energizing coils of said reversing contactors, said energizing meanscomprising control circuits including pushbuttons at the landings; adelayed-action non-interierence switch having contacts in series withthe energizing circuits for said landing pushbuttons, means foractuating said non-interference switch when either of the reversingcontactors is energized, to open its contacts, whenever one of thereversing contactors is energized, and quick-acting means for shuntingsaid non-interference switch contacts when either' or the reversingcontactors is energized.

17. A pushbutton elevator-control system; comprising, in combinationwith an elevator car and a reversible electric elevator motor;electromagnetic up and down reversing contactors, energizing means forthe energizing coils of said reversing contactors, said energizing meansconiprising control circuits including pushbuttons at the landings; aretarded non-interference switch having contacts in series with theenergizing circuits or said landing pushbuttons, a resilient mechanicalconnection between said non-interference switch and the reversingcontactors whereby said non-interference switch is lifted whenevereither one of the reversing contactors is lifted into energizedposition, and a time-delay device for retarding the lowering of saidnoninterference switch upon the deenergization of the energizedcontactor, and quick-acting means for shunting said non-interferenceswitch contacts when either of the reversing contactors is energized.

18. A pushbutton control-system for an electric elevator comprising acar, barriers for the safeguarding of people, and barrier-operatedswitches for the prevention of elevator-movement when said barriers arenot properly positioned, characterized by electromagnetic up and downreversing contactors having energizing coils, main contacts for theelevator motor circuit, and a normally open auxiliary contact;energizing means for the energizing coils of said reversing contactors,said energizing means cornprising control circuits including pushbuttonsat the landings, a retarded non-interference switch having contacts inseries with the energizing circuits for said landing pushbuttons, amechanical connection between said non-interference switch and thereversing contactors whereby said noninterierence switch is liftedwhenever either one of the reversing contactors is lifted into energizedposition, a dashpot for retarding the lowering of said non-interferenceswitch upon the deenergization of the energized contacter, andconnections for connecting each of the normally open auxiliary contactsof the two reversing contactors in parallel to said non-interferenceswitch.

19. The invention as specified in claim 1, characterized by long-stroke,double-contact down buttons at the several landings, connected in serieswith each other, in order, and long-stroke double-contact up buttons atthe several landings, connected in series with each other, in order,whereby, upon the simultaneous depression of two up landing buttons, ortwo down landing buttons,.the car is under the control of the buttonclosest to the source of supply.

20. A constant-pressure pushbutton electric control system for elevatorscomprising up and. down control-circuit means, a supply circuittherefor, double-contact up buttons at the several landings, energizedfrom said supply circuit in series with each other, in order, forenergizing said up control-circuit means when an up button is depressed,and double-contact down buttons at the several landings, energized iromsaid supply circuit in series with each other, in order, for energizingsaid down control-circuit means when a down button is depressed,whereby, upon the simultaneous depression of two up landing buttons, ortwo down landing buttons,

the car is under the vcontrol of the button closest to the source ofsupply.

21. A constant-pressure pushbutton electric control system for elevatorscomprising up and down control-circuit means, a supply Circuit therefor,double-contact up buttons at the several landings, energized from saidsupply circuit in series with each other, in order, starting with thelowest landing, for energizing said up control-circuit means when an upbutton is depressed, and double-contact down buttons at the severallandings, energized from said supply circuit in series with each other,in order, starting with the top landing, for energizing said downcontrol-circuit means when a down button is depressed, whereby upon thesimultaneous depression of two up landing buttons, or two down landingbuttons, the car is under the control of the button closest to thesource of 511191313.

' HARRY BENJAMIN GOLDMAN.

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